1. Field of the Invention
The invention relates to novel o-aminophenolcarboxylic acids and o-aminothiophenolcarboxylic acids, which are also jointly abbreviated to o-amino(thio)phenolcarboxylic acids, and to a process for their preparation.
o-Aminophenolcarboxylic acids are needed, in particular, for the preparation of high-temperature-stable polymers, such as polybenzoxazoles (PBOs) and their precursors. Compared with the preparation of polybenzoxazoles or PBO precursors from bis-o-aminophenols and dicarboxylic acids, the use of o-aminophenolcarboxylic acids has significant advantages. For example, an o-aminophenolcarboxylic acid can be reacted with itself, i.e. a second monomer is not absolutely necessary for the polymerization. This allows purity monitoring and storage to be simplified. In addition, the stoichiometry is predefined, i.e. errors in the calculation or weighing-out of the reactants, as can occur in the reaction of bis-o-aminophenols with dicarboxylic acids, are excluded if o-aminophenolcarboxylic acids are used. Furthermore, the nature of the monomer used has a strong effect on the property profile of the PBO precursor or polybenzoxazole prepared therewith. For example, not only the thermal, electrical and mechanical behavior, but also the solubility and hydrolysis stability and numerous other properties of the polymer are greatly affected by the monomer used in the preparation.
PBO precursors in the form of a photosensitive composition can be structured inexpensively by direct methods, i.e. without an auxiliary resist. Compared with other dielectrics which can be photostructured directly, such as polyimide (PI) and benzocyclobutene (BCB), PBO precursors offer the advantage of positive structurability and aqueous-alkaline development (see EP 0 023 662 B1 and EP 0 264 678 B1). To this end, the PBO precursors used must be substantially transparent at the exposure wavelength and sufficiently soluble in the developer, which preferably contains no metal ions. Like polyimides, polybenzoxazoles also have the major advantage that they--compared with the cyclized final product--as readily soluble precursors, can be applied to a substrate and then cyclized, during which the solubility and thus the sensitivity to solvents and other process chemicals decreases greatly.
Besides good solubility of the precursors, advantages for the use of polybenzoxazoles in microelectronics are low moisture absorption and a good planarization capacity. Production of components using a dielectric which produces good planarization allows expensive polishing procedures (chemical mechanical polishing, CMP) to be avoided.
o-Aminophenolcarboxylic acids are disclosed, for example, in GB 811,758 and GB 1,283,476. In PBO films produced from the known monomers, the water absorption in boiling water after 24 h is 0.77%. No mention is made of the planarization behavior of the polymers produced after cyclization on the substrate or their suitability as base polymers for compositions which can be photostructured positively.